KCNQ channels as therapeutic targets

ABSTRACT

The present disclosure relates to methods and compositions for modulating the activity of KCNQ channels as a means for reducing the effects of aberrant KCNQ channel function associated with epilepsy, deafness and arrhythmias including but not limited to, Long-QT syndrome (“LQTS”), and atrial fibrillation. The present disclosure also relates to the discovery of certain regions of KCNQ channels that interact with various channel stimulating molecules such as, ATP, and PIP 2 , as well as KCNQ channel domains that effect voltage dependant channel activation. The disclosure is also directed to the use of small molecules to modulate KCNQ channel activity in a cell. Moreover, the present disclosure relates to the therapeutic effects of treating a subject with modulators of KCNQ channel activity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.61/788,794, filed Mar. 15, 2013, the entire contents of which areincorporated herein by reference.

GOVERNMENT INTEREST

The present disclosure was made with government support under grantnumbers HL70393, NS060706, HL094410, and GM088517 awarded by theNational Institutes of Health. The government has certain rights in thedisclosure.

INCORPORATION BY REFERENCE OF SEQUENCE LISTING

The Sequence Listing in the ASCII text file, named as29866_sequencelisting.txt of 16 KB, created on Mar. 14, 2014, andsubmitted to the United States Patent and Trademark Office via EFS-Web,is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to methods and compositions formodulating the activity of KCNQ channels as a means for reducing theeffects of aberrant KCNQ channel function associated with epilepsy,deafness and arrhythmias including but not limited to, long-QT syndrome(“LQTS”), and atrial fibrillation. In particular, the present disclosurerelates to the discovery of certain regions of KCNQ channels thatinteract with various channel stimulating molecules such as,adenosine-5′-triphosphate (“ATP”), and phosphatidylinositol4,5-bisphosphate (PIP₂), as well as KCNQ channel domains that effectvoltage dependant channel activation. The disclosure is also directed tothe use of small molecules to modulate KCNQ channel activity. Moreover,the present disclosure relates to the therapeutic effects of treating asubject with modulators of KCNQ channel activity.

BACKGROUND OF THE DISCLOSURE

Voltage activated KCNQ potassium (“K⁺”) channels, provide the molecularbasis for slowly activating delayed-rectifier K⁺ (I_(Ks)) current in theheart, M-currents in neurons which regulate the firing rate of neuronsin the central nervous system and potassium currents in cochlear haircells. I_(Ks), is composed of an or subunit, KCNQ1, and a β subunit,KCNE1 (also known as minK) (see Sanguinetti, M C. et al., Nature (1996)384: 80-83.), while heteromultimers of KCNQ2, KCNQ3 and KCNQ5 subunitsform the basis for the M-channel and KCNQ4 channels form K⁺ currents ofthe cochlear outer hair cells and vestibular utricle in the inner ear.Mutations within the KCNQ channel proteins, KCNQ1-5 (otherwise known asKv7.1-5 or KvLQT1-5) are associated with cardiac arrhythmias (see Wang,Q. et al., Nat. Genetics (1996)12:17-23; Tester, D J. et al., HeartRhythm. (2005) 2: 507-517), epilepsy (see Brown, D A., J. Physiology(2008) 586: 1781-1783; Singh, N A. et al., Nat. Genetics (1998)18:25-29) and deafness (see Brown D A. (2008)).

The crystal structures of several voltage-gated potassium channels havebeen elucidated and extensively studied (see Jiang, Y. et al., Nature(2003) 423:33-41; Long S B. et al Science. (2005) 309: 897-908), howeverstructural modeling of KCNQ channels is incomplete. Although KCNQchannels are structurally similar to other voltage-gated K+ channels,the crystal structure has not yet been solved leading to conflictingresults in the literature regarding the characterization of essentialPIP2 and ATP binding domains as well as the voltage dependant activationmotifs. See Thomas, A M. et al., J. Biol. Chem. (2011) 286(3):2088-100;Hernandez, C C. et al., J. Gen. Physiol. (2008) 132: 361-381).

SUMMARY OF THE DISCLOSURE

The present disclosure provides a method for modulating KCNQ channelactivity of a cell. In an embodiment of the present disclosure the KCNQchannel activity of a cell is increased by contacting the cell with anagent that binds to a portion of a KCNQ channel, including but notlimited to, KCNQ1, KCNQ2, KCNQ3, KCNQ4, KCNQ5, or KCNE1 in an amounteffective to increase KCNQ channel activity of a cell. In certainembodiments, the agent is a small molecule including but not limited toC28 and C4. In an embodiment of the present disclosure the KCNQ channelactivity of a cell is decreased by contacting the cell with an agentthat binds to a portion of a KCNQ channel, including but not limited to,KCNQ1, KCNQ2, KCNQ3, KCNQ4, KCNQ5, or KCNE1 in an amount effective todecrease KCNQ channel activity of a cell. In certain embodiments, theagent is a small molecule including but not limited to C29.

In other embodiments, the small molecule binds to a KCNQ channel orsubunit thereof contacting, at least one of the following amino acidsequences or a fragment or segment thereof; a non-limiting example ofsaid amino acid sequence corresponds with the S2-S3 linker domain ofhuman, rat, mouse, or rabbit KCNQ1 (amino acid residues 177-200), KCNQ2(amino acid residues 147-170), KCNQ3 (amino acid residues 166-191),KCNQ4 (amino acid residues 150-178), KCNQ5 (amino acid residues 178-206)including variations or segments thereof.

In another embodiment the small molecule binds to a KCNQ channel orsubunit thereof, contacting at least one of the following amino acidsequences or a fragment or segment thereof; a non-limiting example ofsaid amino acid sequence corresponds with the S4-S5 linker domain ofhuman, rat, mouse, or rabbit KCNQ1 (amino acid residues 237-262), KCNQ2(amino acid residues 207-232), KCNQ3 (amino acid residues 225-250),KCNQ4 (amino acid residues 213-238), KCNQ5 (amino acid residues 241-266)including variations or segments thereof.

In yet another embodiment the small molecule binds to a KCNQ channel orsubunit thereof, contacting at least one of the following amino acidsequences or a fragment or segment thereof; a non-limiting example ofsaid amino acid sequence corresponds with the S6-C-terminal linkerdomain of human, rat, mouse, or rabbit KCNQ1 (amino acid residues346-370), KCNQ2 (amino acid residues 311-335), KCNQ3 (amino acidresidues 339-363), KCNQ4 (amino acid residues 317-341), KCNQ5 (aminoacid residues 345-369) including variations or segments thereof.

In yet another embodiment the small molecule binds to a KCNE1 subunit ofthe I_(Ks) channel by contacting at least one of the following aminoacid sequences or a fragment or segment thereof; a non-limiting exampleof said amino acid sequence is amino acid residues 67-73 of human, rat,mouse, or rabbit KCNE1.

In yet another embodiment the small molecule binds to a KCNQ channel orsubunit thereof, contacting at least one of the following amino acidsequences or a fragment or segment thereof; a non-limiting example ofsuch an amino acid sequence corresponds with the C-terminal domain ofhuman, rat, mouse, or rabbit KCNQ1 (amino acid residues 369-407), KCNQ2(amino acid residues 334-372), KCNQ3 (amino acid residues 362-400),KCNQ4 (amino acid residues 340-378), KCNQ5 (amino acid residues 368-404)including variations or segments thereof.

In yet another embodiment the small molecule binds to a KCNQ channel orsubunit thereof, contacting at least one of the following amino acidsequences or a fragment or segment thereof; and modulates theinteraction between the S2 and S4 domain of a KCNQ protein. The aminoacid sequence(s) that correspond with the S2 domain of human, rat,mouse, or rabbit KCNQ1 are amino acid residues 155-177, for KCNQ2 areamino acid residues 125-146, for KCNQ3 are amino acid residues 144-165,for KCNQ4 are amino acid residues 131-152, KCNQ5 are amino acid residues159-180, including variations or segments thereof. The S4 domain ofhuman, rat, mouse, or rabbit KCNQ1 includes amino acid residues 223-246,the S4 domain of human, rat, mouse, or rabbit KCNQ2 includes amino acidresidues 193-216, the S4 domain of human, rat, mouse, or rabbit KCNQ3includes amino acid residues 212-234, the S4 domain of human, rat,mouse, or rabbit KCNQ4 includes (amino acid residues 199-222), and theS4 domain of human, rat, mouse, or rabbit KCNQ5 includes (amino acidresidues 227-250) including variations or segments thereof.

Small molecules that bind to homologs, analogs and fragments of theseamino acid sequences are also contemplated by the present disclosure asmodulators of KCNQ channel activity.

In an embodiment of the disclosure, the cell is a neural cell, includingbut not limited to a neuron. In another embodiment, the cell is acardiac cell, including but not limited to, a myocyte. In anotherembodiment, the cell is an outer hair cell of the cochlear.

In certain aspects of the present disclosure is directed to methods andcompositions for modulating KCNQ channel activity in a subject in needthereof, by administering an effective amount of an agent that modulatesthe activity of a KCNQ channel or a subunit thereof. The presentdisclosure provides specific compositions containing at least one KCNQchannel binding molecule that modulates at least one KCNQchannel-mediated biological activity in an organism, including humans.

In one embodiment of the present disclosure the composition is a peptidethat binds a KCNQ channel or a subunit thereof. In yet anotherembodiment of the present disclosure, said composition is a smallmolecule that functions in the same manner as a KCNQ channel effector,including but not limited to ATP, or PIP₂ to modulate KCNQ channelactivity. In yet another embodiment, the agent is a nucleic acid. Thenucleic acid may be an siRNA, or shRNA. Nucleic acid molecules codingfor any peptide that will interact with any of the amino acid sequencesreferenced herein, the expression vectors which include any of suchnucleic acid molecules, as well as related host cells containing suchnucleotide sequences or vectors, are also contemplated by the presentdisclosure.

These and other embodiments of the disclosure will be readily apparentto those of ordinary skill in view of the disclosure herein

BRIEF DESCRIPTION OF DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1. (A) Sequence of S2 and S4 amino acid domains comprising thevoltage gating sensor domain of I_(Ks) channel showing conservednegatively charged amino acid residues in S2 and positively chargedresidues in S4 (bold). (B) Currents from various E1 mutations tonegative or neutral residues in I_(Ks) channels (Scale: 4 μA). (C) G-Vrelationship from mutations in (C). Gray line represents WT I_(Ks).Error bars represent standard error of the means. (D) S4 mutations toglutamate restore E1R current. Currents were recorded from doublemutations (Scale: 6 μA). (E) Peak current amplitudes in (A) wereaveraged for each mutation. Error bars represent standard error of themeans. (F) Current from E1R paired with S4 residues mutated to glutamatecoexpressed with KCNE1 (Scale: 20 μA). (G) Peak current amplitudes in Cwere averaged for each mutant. Error bars represent standard error ofthe means. See Wu, D. et al., J. Gen. Physiol., (2010) 135:595-606.

FIG. 2. ATP dependent activation of I_(Ks) channels. (A) KCNQ1+KCNE1(I_(Ks)) currents in inside-out patches run-down or run-up in 0 (red),0.5 (green) and 5 (blue) mM ATP after patch excision. Voltage wasstepped from a holding potential of −80 to +80 mV and then back to theholding potential. I_(t) and I₀ in the right panel are tail currentamplitudes. The current immediately after patch excision is black inleft panels and I₀ in the right panel. (B) ATP dose response of WT(black) and Q357R (red) I_(Ks). Solid curves are fits to the Hillequation with Hill coefficient 1 and 1.1, and EC₅₀ 1.66 and 9.60 mM forWT and Q357R I_(Ks), respectively. Dashed curves are the fitting of themodel in FIG. 4D. (C) Currents of WT (left) and Q357R (center) I_(Ks)recorded from inside-out patches and G-V relations after patch excisionin solutions containing various ATP concentrations. Solid curves arefits of Boltzmann Equation (see Methods) with V_(1/2) and slope factor:WT, 25.2±2.5 mV, 25.6±1.4 (0.5 mM ATP, black); 23.6±3.6 mV, 27.8±2.2 (20mM ATP, blue); Q357R: 53.2±2.5 mV, 27.3±1.3 (0.5 mM ATP, red); 28.8±2.6mV, 26.4±2.1 (5 mM ATP, green). n=6 for all experiments. Dashed curvesare the fitting of the model in FIG. 4D. (D) Normalized ATPdose-response of WT I_(Ks) channel activation in control solution(black), 5 μM PIP₂ (green), 100 μM Ca²⁺ (red), and S27D/S92D I_(Ks) incontrol solution (blue). In control solution, PIP₂=100 μM and Ca²⁺=0.5nM. See Example 12. Five and 100 μM PIP₂ are 50% and 100% of saturationfor I_(Ks) channel activation, respectively.

FIG. 3. ATP binding to KCNQ1. (A) I_(Ks) current amplitude inintracellular solutions containing 1.5 mM of various nucleotides: ATP(blue), n=12, GTP (green), n=6; AMP-PNP (pink), n=4; ADP (red), n=4; AMP(purple), n=5; and no nucleotide control (black), n=6. The experimentalprotocol is the same as in FIG. 2A. (B) Western blot to detect AB11labeling of channel proteins. Upper: channel proteins pulled down withavidin beads after UV light photo-cross-linking of the biotin-containingAB11. Bottom: channel proteins pulled down with avidin beads afterbiotin treatment of intact cells to detect expression in the membrane.Antibody against KCNQ1 was used in lanes with uninjected, I_(Ks) andKCNQ1; antibodies against KCNQ2 and KCNQ3 were used in lanes with KCNQ2and KCNQ3, respectively. (C) Whole-cell currents of WT and chimericKCNQ1 and KCNQ2/KCNQ3 channels in response to depolarizing voltagepulses (top) and time dependence of current amplitude after inside-outpatch excision without application of intracellular ATP (bottom). WTI_(Ks) (black), n=6; WT KCNQ2/KCNQ3 (blue), n=3; Q2ctQ1/Q3ctQ1 (red),n=4. (D) Cartoon of the key region in KCNQ1 protein for ATP interaction(top), and EC₅₀ of ATP dose response of the key mutant I_(Ks) channels.Asterisk: no current expression. (E) Whole-cell currents of interestedmutations. (F) Western blot to detect AB11 labeling of interestedchannel proteins.

FIG. 4. ATP is required for pore opening. (A) Voltage clamp fluorometry(VCF) recordings of the WT and ATP-binding disruptive mutant I_(Ks)channels. Left: whole-cell current (top) and fluorescence signal(bottom) of WT (black), W379S (red) and R380S/R397W (green) in responseto a series of voltage pulses with increasing voltages. Right:steady-state fluorescence changes versus voltage (F-V). Smooth curvesare Boltzmann fits to the data with V_(1/2) and slope factor for WT,−50.4±1.2 mV, 14.6±0.9; W379S, −51.3±1.2 mV, 14.2±1.1; and S380S/R397W,49.2±0.6 mV, 14.2±0.9. (B) Left: VCF recordings of Q357R (black) andQ357R/R380S/R397W (red). Right: F-V relations and Boltzmann fits withV_(1/2) and slope factor for Q357R, −43.2±1.2 mV, 23.2±1.2; andQ357R/R380S/R397W, 44.1±0.8 mV, 22.1±0.9. (C) G-V relations of I_(Ks) WT(black), R380S (green), K393M (blue), and R397W (red). Smooth curves areBoltzmann fits with V_(1/2) and slope factor for WT, 26.4±1.2 mV,11.2±0.9; R380S, 27.7±1.2 mV, 10.1±1.3; K393M, 25.4±1.1 mV, 10.9±1.1;and R397W, 30.7±1.2 mV, 14.1±1.3. (D) The scheme of voltage and ATPdependent activation of I_(Ks) channels. In this conceptual model,voltage sensor movements are simplified as one transition between theresting (V black) and activated (V red) state, which is not affected byATP binding; the transition of the pore from closed (P black) to theopen (P red) state can happen only after voltage sensor activation andATP binding. K1 and L(V) for the WT and Q357R I_(Ks) obtained fromfittings to ATP dose responses (FIG. 2B) and G-V relations at variousATP concentrations (FIG. 2C) are 300 M⁻¹ and 4.5×10⁻⁴exp(0.94 VF/RT) (V:voltage, F: Faraday Constant, R: gas constant and T: absolutetemperature), and K2 for WT and Q357R I_(Ks) is 1287 and 350,respectively. For all experiments n=6-9.

FIG. 5. Measurement of I_(Ks) in guinea pig ventricular myocytes at 3 mMinternal ATP. Time dependent currents are measured in the absence andpresence of chromanol 293b, a blocker of I_(Ks) channels. The currentmeasurements are taken from control channels (Con, top left) andchromanol sensitive channels (top right) in the absence of chromanol293b and in the presence of 3 mm internal ATP (Chromanol 293b (10 microM), middle right).

FIG. 6. Measurement of I_(Ks) in guinea pig ventricular myocytes at 0 mMinternal ATP. The chromanol 293b sensitive current is plotted as afunction of time after patch formation. At all time points (5 min, topleft; 10 min, middle left; 15 min, bottom left; 20 min, top right; 25min, middle right) the chromanol 293b sensitive current is smaller thanthe chromanol sensitive current shown in FIG. 5 (top right) and currentruns down in a time dependent manner.

FIG. 7. Comparison of the action potentials of I_(Ks) current in guineapig ventricular myocytes at both 10 mM (top) and 3 mM (bottom) internalATP concentrations (10 mM ATP concentration in the patch pipettesolution, 3 mM ATP concentration in the patch pipette solution) in thepresence and absence of chromanol 293b (closed circle). A higherconcentration of ATP (top) shows a greater effect of chromanol 293b asshown by the shift in channel activity due to an increase in I_(Ks)channel current density. Revealing that ATP shortens the ventricularaction potential duration in cardiac myocytes.

FIG. 8. Effects of mutations at the VSD-PD interface. (A) Sequencealignment of KCNQ channels S2-S3, S4-S5 linkers and proximal C-terminus.Highlighted residues were individually neutralized in WT KCNQ1 (Kv7.1).(B) Raw current at −100 to +40 mV. (C) Current amplitude (at +20 mV)normalized to WT. Color code: blue, I/Iwt<0.5; green, 0.5<I/Iwt<1; red,I/Iwt>1. (D) Western blot of biotinilated membrane proteins. CTL Mem,CTL Lys: membrane fraction and whole cell lysate from uninjected cells.(E) ΔF/F (−80 to +60 mV). (F) Current rundown after inside-out patchexcision in the presence of KCNE1. Current in response to repeated +80mV pulses (left). Normalized tail current amplitude (right). (G) 50%rundown time versus I/Iwt. From left to right: K362N, K358N, WT, R249Q,K183N, R249E.

FIG. 9. Mutations at the VSD-PD interface alter coupling. Colors as inFIG. 8C. (A-C) F-V relationships of psWT/mutation (solid, filled) andpsWT/L353K/mutation (dotted, open). (D) The change in z*V_(1/2) betweenpsWT/mutation and psWT/L353K/mutation versus I/Iwt. From left to right:H363N, R195Q, R360Q, R366Q, K362N, R192Q, K358N, WT, K3358E, R360E,K196N. z*V_(1/2) is a measure of the energy required to activate theVSD, where z and V_(1/2) were obtained by fitting the Boltzmannequation.

FIG. 10. Effects of PIP₂ depletion on voltage-dependent gating. VCFrecordings of psWT (black) or psWT+CiVSP (blue). The protocols weredesigned to deplete PIP₂ in the presence of CiVSP by first applying sixvoltage pulses. (A) Voltage protocol used, the membrane potential isstepped from a holding potential of −80 mV to various test potentials(−120 to +80 mV) for 4 seconds and then to +60 mV for 2 seconds toactivate CiVSP. (B) The membrane is stepped from a holding potential of−80 mV to +60 mV for 2 seconds to activate the VSDs and CiVSP. Themembrane potential is then repolarized to various test potentials (−140to +60 mV) to track the return of the VSD to the resting state. (C, D)Raw Currents. (E,F) ΔF/F. Signals are normalized to that at the end ofthe +60 mV pulse (E) or prepulse (F). (G,H) Normalized F-Vrelationships. Signals at the end of the 4 s test pulses are normalizedto that at 0 mV and plotted versus test voltage. (I) Fast (left) andslow (right) tau of the double exponential fit to the fluorescent signalchanges caused by depolarization (−40 to +80 mV) or repolarization (−140to −100 mV) are plotted versus test voltage.

FIG. 11. Small molecule C29 selectively inhibits KCNQ channels composedof KCNQ1 and KCNE1. 100 μM concentrations of C29 inhibits I_(Ks) channelcurrent more effectively than KCNQ1 alone. Currents were induced by theapplication of a +60 mV pulse.

FIG. 12. Small molecule C28 modulates KCNQ channel activity. (A) C28increases channel current in M-channels composed of KCNQ2 and KCNQ3subunits. M-currents were measured at +40 mV, where G-V relation in thepresence or absence of C28 is saturated. (B) The G-V relations in thepresence or absence of C28. V_(1/2) and the slope for KCNQ2/3 in theabsence of C28 are −28.1±0.2 mV and 7.05±0.16 mV, respectively. V_(1/2)and the slope for KCNQ2/3 in the presence of C28 are −45.9±0.4 mV and8.21-0.37 mV, respectively. (C) The EC50 of the change in V_(1/2)(V_(1/2) control−V_(1/2C28)) for KCNQ2/3 is 4.4±0.3 μM, and the Hillcoefficient is 0.92±0.06.

FIG. 13. Small molecule C28 modulates KCNQ1 and I_(Ks) channel activity.(A) C28 increases current amplitudes. (B) C28 shifts G-V relations. Thesmooth curves are Boltzmann fit to data with V_(1/2) and slope of−40.1±1.0 mV and 10.6±1.0 mV for KCNQ1 channels, and V in and a slope of−86.3±1.2 mV and 14.8±1.2 mV KCNQ1 channels with 10 M C28. The V_(1/2)and slope is −23.9±0.9 mV and 12.9±0.8 mV for I_(Ks) channels andV_(1/2) and a slope of −32.2±1.0 mV and 18.9±1.1 mV I_(Ks) channels inthe presence of 10 μM C28. (C) Dose responses of G-V shift induced byC28. The EC50 of the change in V_(1/2) (V_(1/2) control−V_(1/2C28)) forKCNQ1 is 15.8±8.5 μM, and 12.7±11.4 μM for I_(Ks) channels. Takentogether, C28 shifts I_(Ks) in the negative direction in a dosedependent manner and is effective on both KCNQ1 and I_(Ks).

FIG. 14. Small molecule C4 (Acid Orange 3(#4)) modulates KCNQ1 channelactivity. The effects of C4 on KCNQ channels alone (right) and I_(Ks)channels (left). The upper panel shows raw currents through KCNQchannels where voltage was stepped from a holding potential of −80 to+40 mV. The middle panel reveals the time dependence of currentamplitude after the drug is applied. The lower panel shows the timeconstants (Tau) exponential fit to channel deactivation

DETAILED DESCRIPTION OF THE DISCLOSURE

Ion channels permit flows of selective ions across cell membranes andregulate the membrane potential and the duration of action potentials,thereby controlling many basic biological processes such as contractionsof cardiac, skeletal and smooth muscles and transport of nutrients andhormones. See Zaydman, M A. et al., Chem. Rev. 112:6319-6333. (2012).

Voltage activated KCNQ K⁺ channels, KCNQ1-5 (also known as Kv7.1-5), arethe molecular basis of I_(Ks) currents in the heart, M-currents in manytypes of neurons, and K⁺ currents in cochlear hair cells that regulatethe cardiac action potential duration, neuronal discharge and synaptictransmission, and endolymph potassium homeostasis; mutations of thesechannel proteins are associated with cardiac arrhythmias, epilepsy anddeafness. See Hill, B. Ion Channels of Excitable Membranes. 3^(rd) ed.(2001). The slowly activating delayed-rectifier potassium current,I_(Ks), is essential for the termination of cardiac action potentialsand the maintenance of a normal heart rhythm. See Hill (2001). TheI_(Ks) channel is co-assembled by KCNQ1 and KCNE1 subunits. KCNQ1 isalso referred to as Kv7.1 or KvLQT1, and KCNE1 is also known as minK.The α-subunit, KCNQ1, forms the conductance pore of I_(Ks). The3-subunit, KCNE1, is an auxiliary protein that associates with andmodulates the activity of KCNQ1. See Sun, X., et al., Front.Pharmacology. 3:63 (2012). These physiologically important channels allrequire PIP₂ in order to open, and the cardiac I_(Ks) channel, formed byKCNQ1 and auxiliary subunit KCNE1 (see Sanguinetti et al. (1996)), alsorequires intracellular ATP for activation. Although PIP₂ and ATP arevital for the function of KCNQ channels, the molecular mechanisms ofregulation by these signaling molecules are not clear; central questionssuch as the location and identity of PIP₂ and ATP binding sites and howthese molecules alter channel function after binding still remainunclear. Previous studies and our data show that a number of mutationsin KCNQ1 that are associated with long-QT syndrome (LQTS). Applicants'disclosure reveals that a reduction in I_(Ks) channel activity byaltering PIP₂ or ATP sensitivity leads to LQTS and provides themethodological basis for PIP₂ and ATP mediated regulation of KCNQchannels in their native cells.

KCNQ1 alone can form a functional voltage-gated potassium (Kv) channel.Kv channels are formed by the co-assembly of four α-subunits, eachconsisting of six transmembrane helices (S1-S6). The first four helices(S1-S4) form the voltage-sensing domain (VSD) and S5-S6 form the poredomain (PD). The S4 segment contains conserved basic residues. Membranedepolarization exerts force on these charged residues, moving S4outward, which then induce the opening of the pore. To date, the crystalstructure of full-length KCNQ1 has not been solved.

Mutations in the KCNQ1 gene are associated with long-QT syndrome, acongenital disorder that is characterized by a prolongation of the QTinterval on electrocardiograms (ECGs), and increase the risk of suddendeath from cardiac arrhythmias. The reduction of the I_(Ks) currents bythese mutations prolongs ventricular action potentials, thereby the QTinterval. The I_(Ks) channel therefore serves as a valuable drug targetand the potentiators of I_(Ks) can be used for treating cardiovasculardiseases. During Kv channel formation, four subunits co-assemble to forma tetrameric complex with a central pore built from the PDs of all foursubunits and the four VSDs located peripheral to the central pore.Voltage dependent activation involves three general molecular events: 1)VSD movements from the resting state to the activated state in responseto membrane depolarization, 2) propagation of VSD activation to the PDthrough the interactions between VSD and PD, known as coupling, and 3)pore opening. See Tombola, F., et al. Annu. Rev. Cell Dev. Biol.22:23-52. (2006).

The present disclosure elucidates the molecular mechanism governing KCNQchannel activity and shows that PIP₂ is not required for VSD movementsbut is required for the coupling between VSD and PD, and that ATPdirectly binds to KCNQ1 for channel activation. Thus, the presentdisclosure identifies and isolates the essential domains within KCNQchannels that govern channel activity, including but not limited to,voltage activation, PIP₂ binding and ATP binding. Therefore, methods andcompositions for modulating the activity of KCNQ channels are providedas a means for treating a subject in need thereof.

Cardiac arrhythmias result from an increase in the duration of theventricular action potential. This increase in ventricular actionpotential induces LQTS, which leads to a type of arrhythmia calledtorsade de pointes resulting in sudden death. In a small number of casesit is inherited, while in the vast majority it is acquired due topharmacotherapy. This side effect of pharmacotherapy has removedpromising drug candidates from market consideration and remains aserious concern with others that are currently in use. I_(Ks) exists inmammalian atrial and ventricular myocytes providing for therepolarization of cardiac action potential. Atrial Fibrillation (AF) isan arrhythmia that has become increasingly prevalent in our agingpopulation, and repolarization of the atrial action potential is in partdue to I_(Ks).

Novel targets of the present disclosure, which encompass regions of theI_(Ks) channel, have been defined herein and used to create noveltherapeutic approaches to treating LQTS. Blockers of this same channelhave therapeutic potential for a common arrhythmia of the atrium, atrialfibrillation said blockers include but are not limited to2-[4-(3,4-Dimethylphenoxy)phenyl]-1,3-dioxoisoindoline-5-carboxylic acid(C29). As, the α-subunit of the I_(Ks) channel belongs to the KCNQfamily and the M-current is composed of heteromultimers of three othermembers of the KCNQ family (KCNQ2, 3 and/or KCNQ5) and one of the K⁺channels in the ear is composed of KCNQ4, and thus the therapeuticagents of the present disclosure are also effective in treating epilepsyand congenital deafness, respectively.

Particularly, useful compositions for modulating KCNQ channels include,but are not limited to, disodium;3-[[4-hydroxy-9,10-dioxo-2-(4-sulfonatoanilino)anthracen-1-yl]amino]benzenesulfonate(C28), bis(2-pyridylthio)zinc 1,1′-dioxide (zinc pyrithione) and ethylN-[2-amino-4-[(4-fluorophenyl)methylamino]phenyl]carbamate (Retigabine).

The novel targets of the present disclosure encompass regions of KCNQ2-5proteins and the channels composed thereof. Thus, agonists of channelscontaining KCNQ2-5 are used to alleviate the physiological conditionsassociated with KCNQ channel dysfunction via the use of therapeuticagents that act to enhance channel function, a non-limiting example isthe compound; sodium; 2-anilino-5-(2,4-dinitroanilino)benzenesulfonate(C4), which can be used to treat diseases including, epilepsy anddeafness. See FIG. 14.

Therapeutic Targets

According to the present disclosure there are small molecules thatmodulate KCNQ channel activity of a cell. In the present disclosure thesmall molecules modulate KCNQ channel activity of a cell by contacting aportion of a KCNQ channel, including but not limited to, KCNQ1, KCNQ2,KCNQ3, KCNQ4, KCNQ5, or KCNE1. In the present disclosure an effectiveamount of a small molecule will increase or decrease KCNQ channelactivity. Non-exclusive measures of KCNQ channel activity include theability of KCNQ channels or subunits thereof to bind effectors thereof,or the KCNQ channels ability to pass a current.

In one aspect, the agents of the present disclosure modulate KCNQchannel activity by interacting with the amino acid sequence thatcorresponds with the S2-S3 linker domain of human, rat, mouse, or rabbitKCNQ1 (amino acid residues 177-200) for example,SAGCRSKYVGLWGRLRFARKPISI (SEQ ID NO:1); KCNQ2 (amino acid residues147-170) for example, AAGCCCRYRGWRGRLKFARKPFCV (SEQ ID NO:2); KCNQ3(amino acid residues 166-191) for example, AAGCCCRYKGWRGRLKFARKPLCMLD(SEQ ID NO:3); KCNQ4 (amino acid residues 150-178) for example,RVWSAGCCCRYRGWQGRFRFARKPFCVID (SEQ ID NO:4); KCNQ5 (amino acid residues178-206) for example, RIWSAGCCCRYRGWQGRLRFARKPFCVID (SEQ ID NO:5).

In one aspect of the current disclosure, the agents modulate KCNQchannel activity by interacting with an amino acid sequence correspondswith the S4-S5 domain of human, rat, mouse, or rabbit KCNQ1 (amino acidresidues 237-262) for example, RMLHVDRQGGTWRLLGSVVFIHRQEL (SEQ ID NO:6); KCNQ2 (amino acid residues 207-232) for example,RMIRMDRRGGTWKLLGSVVYAHSKEL (SEQ ID NO: 7); KCNQ3 (amino acid residues225-250) for example, RMLRMDRRGGTWKLLGSAICHAHSKEL (SEQ ID NO: 8); KCNQ4(amino acid residues 213-238) for example, RMVRMDRRGGTWKLLGSVVYAHSKEL(SEQ ID NO: 9); KCNQ5 (amino acid residues 241-266) for example,RMVRMDRRGGTWKLLGSVVYAHSKEL (SEQ ID NO:9) including variations orsegments thereof.

In one aspect, the agents of the present disclosure modulate KCNQchannel activity by interacting with an amino acid sequence thatcorresponds with the S6-C-terminal linker domain of human, rat, mouse,or rabbit KCNQ1 (amino acid residues 346-370) for exampleILGSGFALKVQQKQRQKHFNRQIPA (SEQ ID NO: 10); KCNQ2 (amino acid residues311-335) for example, ILGSGFALKVQEQHRQKHFEKRRNP (SEQ ID NO: 11); KCNQ3(amino acid residues 339-363) for example, ILGSGLALKVQEQHRQKHFEKRRKP(SEQ ID NO: 12); KCNQ4 (amino acid residues 317-341) for exampleILGSGFALKVQEQHRQKHFEKRRMP (SEQ ID NO: 13); KCNQ5 (amino acid residues345-369) for example, ILGSGFALKVQEQHRQKHFEKRRNP (SEQ ID NO: 14)including variations or segments thereof.

A preferred modulator of KCNQ channel activity of the present disclosureis a small molecule that interacts with the amino acid domain within theKCNQ1 protein encompassing the sequence RXXXXRX₆₂HRX₉₄K (SEQ ID NO: 15),wherein X_(n) can be any amino acid which includes:

A=Ala=Alanine

R=Arg=Arginine

N=Asn=Asparagine

D=Asp=Aspartate

B=Asx=Asparagine or Aspartate

C=Cys=Cysteine

Q=Gln=Glutamine

E=Glu=Glutamate

Z=Glx=Glutamine or Glutamate

G==Gly=Glycine

H=His=Histidine

I=Ile=Isoleucine

L=Leu=Leucine

K=Lys=Lysine

F=Phe=Phenylalanine

P=Pro=Proline

S=Ser=Serine

T=Thr=Threonine

W=Trp=Tryptophan

Y=Tyr=Tyrosine

V=Val=Valine

Preferably, X_(n) are those amino acids that are homologs of the nativeresidues found in the KCNQ channel protein.

More preferably, X_(n) are those amino acids found in the nativesequence of a vertebrate KCNQ channel protein.

A preferred modulator of KCNQ channel activity of the present disclosureis a small molecule that interacts with the amino acid domain within theKCNQ2, KCNQ4 OR KCNQ5 protein encompassing the sequence RXXXXRX₆₂HXKX₈₈K(SEQ ID NO: 16).

A preferred modulator of KCNQ channel activity of the present disclosureis a small molecule that interacts with the amino acid domain within theKCNQ3 protein encompassing the sequence RXXXXRX₆₁HXKX₉₈K (SEQ ID NO:17).

Yet another preferred modulator of KCNQ channel activity is a smallmolecule that interacts with the amino acid residues within the KCNE1protein encompassing amino acid residues 67-75 of human, rat, mouse, orrabbit KCNE1, for example RSKKLEHSN (SEQ ID NO. 18).

A preferred modulator of KCNQ channel activity of the present disclosureis a small molecule that interacts with the amino acid domain within theKCNE1 protein encompassing the sequence RXKKXXH (SEQ ID NO: 19).

In one aspect, the agents of the present disclosure modulate KCNQchannel activity by interacting with an amino acid sequence thatcorresponds with the C-terminal domain of human, rat, mouse, or rabbitKCNQ1 (amino acid residues 369-397) for example,PAAASLIQTAWRCYAAENPDSSTWKIYIR (SEQ ID NO: 20); KCNQ2 (amino acidresidues 335-362) for example PAAGLIQSAWRFYATNLSRTDLHSTWQY (SEQ ID NO:21); KCNQ3 (amino acid residues 363-389) for examplePAAELIQAAWRYYATNPNRIDLVATWR (SEQ ID NO: 22); KCNQ4 (amino acid residues341-368) for example, PAANLIQAAWRLYSTDMSRAYLTATWYY (SEQ ID NO: 23);KCNQ5 (amino acid residues 369-394) for example,PAANLIQCVWRSYAADEKSVSIATWK (SEQ ID NO: 24) including variations orsegments thereof.

A preferred modulator of KCNQ channel activity of the present disclosureis a small molecule that interacts with the amino acid domain within aKCNQ protein encompassing the sequence WRX₁₂KXXXR (SEQ ID NO: 25).

In one aspect, the agents of the present disclosure modulate KCNQchannel activity by interacting with an amino acid sequence thatmodulates the interaction between the S2 and S4 domain of a KCNQprotein. Non limiting examples of this domain include, the amino acidsequence that corresponds with the S2 domain of human, rat, mouse, orrabbit KCNQ1 comprises amino acid residues 155-177,TLFWMEIVLVVFFGTEYVVRLWS (SEQ ID NO: 26); KCNQ2 (amino acid residues125-146) for example, ALYILEIVTIVVFGVEYFVRIW (SEQ ID NO: 27); KCNQ3(amino acid residues 144-165) for example, WLLLLETFAIFIFGAEFALRIW (SEQID NO: 28); KCNQ4 (amino acid residues 131-152) for example,CLLILEFVMIVVFGLEYIVRVW (SEQ ID NO: 29); KCNQ5 (amino acid residues159-180) for example, CLLILEFVMIVVFGLEFIIRIW (SEQ ID NO: 30); the aminoacid domain that comprises the S4 domain of human, rat, mouse, or rabbitKCNQ1 is amino acid residues 223-246, ATSAIRGIRFLQILRMLHVDRQGG (SEQ IDNO: 31), KCNQ2 (amino acid residues 193-216) for example,ATSALRSLRFLQILRMIRMDRRGG (SEQ ID NO: 32); KCNQ3 (amino acid residues212-234) for example, ATSLRSLRFLQILRMLRMDRRGG (SEQ ID NO: 33); KCNQ4(amino acid residues 199-222) for example, ATSALRSMRFLQILRMVRMDRRGG (SEQID NO: 34); KCNQ5 (amino acid residues 227-250) for example,ATSALRSLRFLQILRMVRMDRRGG (SEQ ID NO: 35), including variations orsegments thereof.

A preferred modulator of KCNQ channel activity of the present disclosureis a small molecule that interacts with the amino acid domain within aKCNQ protein, which includes the sequence RXXRXXXXXR (SEQ ID NO: 36).

A preferred modulator of KCNQ channel activity interacts with an aminoacid sequence encompassing any of the following amino acid residuesR228, R231 and R237 that prevents interaction with amino acid E160 orD160 of a KCNQ protein.

A preferred modulator of KCNQ channel activity interacts with an aminoacid sequence encompassing any of the following amino acid residuesR198, R201 and R207 that prevents interaction with amino acid E130 of aKCNQ protein.

A preferred modulator of KCNQ channel activity interacts with an aminoacid sequence encompassing any of the following amino acid residuesR198, R201 and R207 that prevents interaction with amino acid E130 of aKCNQ protein.

A preferred modulator of KCNQ channel activity interacts with an aminoacid sequence encompassing any of the following amino acid residuesR216, R219 and R225 that prevents interaction with amino acid E149 of aKCNQ protein.

A preferred modulator of KCNQ channel activity interacts with an aminoacid sequence encompassing any of the following amino acid residuesR204, R207 and R213 that prevents interaction with amino acid E136 of aKCNQ protein.

A preferred modulator of KCNQ channel activity interacts with an aminoacid sequence encompassing any of the following amino acid residuesR232, R235 and R241 that prevents interaction with amino acid E1164 of aKCNQ protein.

Small molecules that bind to homologs, analogs and fragments of theseamino acid sequences are also contemplated by the present disclosure asmodulators of KCNQ channel activity.

In an embodiment of the disclosure, the cell is a neural cell, includingbut not limited to, a neuron. In another embodiment, the cell is acardiac cell, including but not limited to, a myocyte. In anotherembodiment, the cell is an outer hair cell of the cochlear.

Therapeutic Treatment

The present disclosure also provides methods and compositions formodulating KCNQ channel activity in a subject in need thereof, byadministering an effective amount of an agent that modulates theactivity of a KCNQ channel or a subunit thereof. The present disclosureprovides specific compositions containing at least one KCNQ channelbinding molecule that modulates at least one KCNQ channel-mediatedbiological activity in an organism, including but not limited to,humans.

The dosage of an agent that is administered to a subject in need thereofmay vary, depending on the reason for use and the individual subject.The dosage may be adjusted based on the subject's weight, the age andhealth of the subject, and tolerance for the compound or composition.

The amount of agent [therapeutic] to be used depends on many factors.Dosages may include about 2 mg/kg of bodyweight/day, about 5 mg/kg ofbodyweight/day, about 10 mg/kg of bodyweight/day, about 15 mg/kg ofbodyweight/day, about 20 mg/kg of bodyweight/day, about 25 mg/kg ofbodyweight/day, about 30 mg/kg of bodyweight/day, about 40 mg/kg ofbodyweight/day, about 50 mg/kg of bodyweight/day, about 60 mg/kg ofbodyweight/day, about 70 mg/kg of bodyweight/day, about 80 mg/kg ofbodyweight/day, about 90 mg/kg of bodyweight/day, about 100 mg/kg ofbodyweight/day, about 125 mg/kg of bodyweight/day, about 150 mg/kg ofbodyweight/day, about 175 mg/kg of bodyweight/day, about 200 mg/kg ofbodyweight/day, about 250 mg/kg of bodyweight/day, about 300 mg/kg ofbodyweight/day, about 350 mg/kg of bodyweight/day, about 400 mg/kg ofbodyweight/day, about 500 mg/kg of bodyweight/day, about 600 mg/kg ofbodyweight/day, about 700 mg/kg of bodyweight/day, about 800 mg/kg ofbodyweight/day, and about 900 mg/kg of bodyweight/day. Routineexperimentation may be used to determine the appropriate value for eachpatient by monitoring the compound's effect on KCNQ channel activity, orthe disease pathology, which can be frequently and easily monitored. Theagent can be administered once or multiple times per day. The frequencyof administration may vary from a single dose per day to multiple dosesper day. Preferred routes of administration include oral, intravenousand intraperitoneal, but other forms of administration may be chosen aswell.

The effective amount of an agent according to the present disclosure maybe administered along any of the routes commonly known in the art. Thisincludes, for example, (1) oral administration; (2) parenteraladministration, for example, by subcutaneous, intramuscular orintravenous injection; (3) topical administration; or (4) intravaginalor intrarectal administration; (5) sublingual or buccal administration;(6) ocular administration; (7) transdermal administration; (8) nasaladministration; and (9) administration directly to the organ or cells inneed thereof.

The effective amount of an agent according to the present disclosure maybe formulated together with one or more pharmaceutically acceptableexcipients. The active ingredient and excipient(s) may be formulatedinto compositions and dosage forms according to methods known in theart. These compositions and dosage forms may be specially formulated foradministration in solid or liquid form, including those adapted for thefollowing: (1) oral administration, for example, tablets, capsules,powders, granules, pastes for application to the tongue, aqueous ornon-aqueous solutions or suspensions, drenches, or syrups; (2)parenteral administration, for example, by subcutaneous, intramuscularor intravenous injection as, for example, a sterile solution orsuspension; (3) topical application, for example, as a cream, ointmentor spray applied to the skin, lungs, or mucous membranes; or (4)intravaginally or intrarectally, for example, as a pessary, cream orfoam; (5) sublingually or buccally; (6) ocularly; (7) transdermally; or(8) nasally.

In the context of the present disclosure, the effective amount of theagent modulating KCNQ channel activity may be administered alone or incombination with one or more additional therapeutic agents (secondtherapeutic entity), regardless of the disease that said secondtherapeutic entity is administered to treat. In a combination therapy,the effective amount of the agent modulating KCNQ channel activity maybe administered before, during, or after commencing therapy with anotheragent, as well as any combination thereof, i.e., before and during,before and after, during and after, or before, during and aftercommencing the additional therapy. For clarity, an agent of the presentdisclosure may be administered in an effective amount in response aprior treatment that brings about the need to modulate KCNQ channelfunction.

In another embodiment of the present disclosure the composition is apeptide that binds a KCNQ channel or a subunit thereof. In yet anotherembodiment of the present disclosure, said composition is a smallmolecule that functions in the same manner as a KCNQ channel effector,including but not limited to voltage, ATP, or PIP₂ to modulate KCNQchannel activity. In yet another embodiment, the agent is a nucleicacid. The nucleic acid may be an siRNA, shRNA. Nucleic acid moleculescoding for any peptide that will interact with any of the amino acidsequences referenced herein, the expression vectors which include any ofsuch nucleic acid molecules, as well as related host cells containingsuch nucleotide sequences or vectors, are also contemplated by thepresent disclosure.

Consistent with the observed properties of the KCNQ channels that arethe subject of this disclosure, an agent of the present disclosure canbe used to inhibit, suppress or cause the cessation of at least one KCNQchannel mediated disease pathology including but not limited to LQTS,epilepsy, deafness, atrial fibrillation and diabetes. See Unoki et al.Nat. Genet. 40:1098-102 (2008); and Holmkvist et al., PLoS One.;4(6):e5872 (2009).

TERMINOLOGY

The term “KCNQ channel” or “KCNQ channels” is employed herein to referany ion channel having at least one KCNQ subunit, including but notlimited to KCNQ1, KCNQ2, KCNQ3, KCNQ4, and KCNQ5. Non-limiting examplesof KCNQ channel(s) include I_(Ks) channels, M-channels, and KCNQ4channels.

The phrase “I_(Ks) channel or I_(Ks) channels” refers to any channelcomposed of KCNQ1 and KCNE1 subunits that form the basis of the slowlyactivating delayed-rectifier potassium current (I_(Ks)) that regulatecardiac action potential duration.

The phrase “M-channel” or “M-channels” refers to any channel composed ofKCNQ2 and/or KCNQ3 subunits or KCNQ5 subunits that regulateneurotransmission and membrane excitability in neural cells.

The phrase “KCNQ4 channel” or “KCNQ4 channels” are composed of one ormore KCNQ4 subunit and form the basis of the cochlear out hair cell andvestibular utricle K⁺ currents (I_(Kn)).

The phrase “modulating the activity” or “modulating the level” isemployed herein to refer to increasing the level or decreasing theactivity of an entity including but not limited to, a channel, peptideor molecule. Non-limiting examples of the activity or level of a channelinclude the density (number of channels/unit area) of the KCNQ proteinin a membrane or the ability of KCNQ channels to function or bindeffectors thereof. The phrase “channel activity” or “channel function”refers to the ability of a channel to pass ionic current, smallmolecule(s), bind effectors, respond to voltage, mechanical force, heat,or light or regulate cellular homeostasis.

The term “channel” or “channels” as referred to in the presentdisclosure includes both 1) pumps that use a source of free energyincluding but not limited to, ATP, ionic gradient or light to drive thetransport of ions or molecules across membranes within or surroundingcells of an organism; and 2) channels, which enable ions or molecules toflow through membranes within or surrounding cells.

The term “voltage dependent activation” refers to the process bywhich 1) a voltage-sensing domain of a KCNQ channel subunit moves fromthe resting to the activated state, for example a voltage sensing domainof the KCNQ1 protein moves to an activated state in response to membranedepolarization; 2) coupling, for example when a voltage-sensing domainof a KCNQ channel protein interacts with the channel pore (pore domain);and 3) opening of the channel pore.

The term “agent” is employed herein to refer to any kind of compound,molecule or ion and any combination thereof. In one embodiment of thedisclosure the agent is a small molecule. In another embodiment of thedisclosure, the agent is a biological molecule, including, but notlimited to, a protein or a peptide or a nucleic acid, or an ion. Inanother embodiment, the nucleic acid is an interfering RNA.

The phrase “effector” or “effectors” refers to any small molecule,protein, ligand, or complex thereof that binds to, or interacts with aKCNQ channel or a subunit thereof. The result of this interaction maymodulate a biological activity including but not limited to, muscle cellfunction, cell contractility, channel activation, neuronal discharge,membrane excitation, cell signaling, enzymatic activity, orprotein-protein interaction.

The term “interfering RNA” is employed herein to refer to smallinterfering RNAs (siRNAs), short hairpin RNAs (shRNAs), microRNAs(miRNAs), antisense oligonucleotides, ribozymes, or any RNA-basedmolecule that interferes with the expression of a protein from itscorresponding gene or modulate the activity of the protein.

In the context of this disclosure, the term “small molecule” refers tosmall organic compounds, including but not limited to, heterocycles,peptides, saccharides, steroids, antibodies and the like. The smallmolecule modulators preferably have a molecular weight of less thanabout 1500 Daltons, and more preferably less than 500 Daltons. The smallmolecules can be modified to enhance efficacy, stability, pharmaceuticalcompatibility, and the like. Candidate modulator compounds fromlibraries of synthetic or natural compounds can be screened. Syntheticcompound libraries are commercially available from a number of companiesincluding Maybridge Chemical Co. (Trevillet, Cornwall, UK), Comgenex(Princeton, N.J.), Brandon Associates (Merrimack, N.H.), Microsource(New Milford, Conn.), and ChemBridge (San Diego, Calif.). Combinatoriallibraries are available or can be prepared according to known synthetictechniques. Alternatively, libraries of natural compounds in the form ofbacterial, fungal, plant and animal extracts are available from e.g.,Pan Laboratories (Bothell, Wash.) or MycoSearch (NC), or are readilyproducible by methods well known in the art. Additionally, natural andsynthetically produced libraries and compounds may be further modifiedthrough conventional chemical and biochemical techniques.

The term “peptide” refers to a linear series of amino acid residueslinked to one another by peptide bonds between the alpha-amino andcarboxy groups of adjacent amino acid residues.

The term “synthetic peptide” is intended to refer to a chemicallyderived chain of amino acid residues linked together by peptide bonds.The term “synthetic peptide” is also intended to refer to recombinantlyproduced peptides in accordance with the present disclosure.

The phrase “subject in need thereof” as used herein refers to anyorganism in need of treatment, or requiring preventative therapy toprevent a condition resulting from lower or higher than normal levels ofKCNQ channel activity in the organism, by the methods of the disclosure.The subject may be a plant or an animal. The subject animal includesfish, birds, or mammals. The subject may be livestock, such as cattle,swine, sheep, poultry, and horses, or pets, such as dogs and cats. In anembodiment of disclosure the subject is a human.

The term “effective amount” is employed herein to refer to the amount ofan agent that is effective in modulating KCNQ channel activity in asubject or cell.

The phrase “pharmaceutically acceptable” is employed herein to refer tothose compounds, materials, compositions, and/or dosage forms which are,within the scope of sound medical judgment, suitable for use in contactwith the tissues of the subject with toxicity, irritation, allergicresponse, or other problems or complications, commensurate with areasonable benefit/risk ratio.

The phrase “pharmaceutically-acceptable excipient” as used herein refersto a pharmaceutically-acceptable material, composition or vehicle, suchas a liquid or solid filler, diluent, carrier, manufacturing aid (e.g.,lubricant, talc magnesium, calcium or zinc stearate, or stearic acid),solvent or encapsulating material, involved in carrying or transportingthe therapeutic compound for administration to the subject. Eachexcipient should be “acceptable” in the sense of being compatible withthe other ingredients of the formulation and not injurious to thesubject. Some examples of materials which can serve aspharmaceutically-acceptable excipients include: sugars, such as lactose,glucose and sucrose; starches, such as corn starch and potato starch;cellulose and its derivatives, such as sodium carboxymethyl cellulose,ethyl cellulose and cellulose acetate; gelatin; talc; waxes; oils, suchas peanut oil, cottonseed oil, safflower oil, sesame oil, olive oil,corn oil and soybean oil; glycols, such as ethylene glycol and propyleneglycol; polyols, such as glycerin, sorbitol, mannitol and polyethyleneglycol; esters, such as ethyl oleate and ethyl laurate; agar; bufferingagents; water; isotonic saline; pH buffered solutions; and othernon-toxic compatible substances employed in pharmaceutical formulations.If desired, certain sweetening and/or flavoring and/or coloring agentsmay be added. Other suitable excipients can be found in standardpharmaceutical texts, e.g. in “Remington's Pharmaceutical Sciences”, TheScience and Practice of Pharmacy, 19^(th) Ed. Mack Publishing Company,Easton, Pa., (1995).

Excipients are added to the agent for a variety of purposes. Diluentsincrease the bulk of a solid pharmaceutical composition, and may make apharmaceutical dosage form containing the composition easier for thepatient and caregiver to handle. Diluents for solid compositionsinclude, for example, microcrystalline cellulose (e.g. Avicel®),microfine cellulose, lactose, starch, pregelatinized starch, calciumcarbonate, calcium sulfate, sugar, dextrates, dextrin, dextrose, dibasiccalcium phosphate dihydrate, tribasic calcium phosphate, kaolin,magnesium carbonate, magnesium oxide, maltodextrin, mannitol,polymethacrylates (e.g. Eudragit®), potassium chloride, powderedcellulose, sodium chloride, sorbitol and talc.

Solid pharmaceutical agents that are compacted into a dosage form, suchas a tablet, may include excipients whose functions include helping tobind the active ingredient and other excipients together aftercompression. Binders for solid pharmaceutical compositions includeacacia, alginic acid, carbomer (e.g. carbopol), carboxymethylcellulosesodium, dextrin, ethyl cellulose, gelatin, guar gum, hydrogenatedvegetable oil, hydroxyethyl cellulose, hydroxypropyl cellulose (e.g.Klucel®), hydroxypropyl methyl cellulose (e.g. Methocel®), liquidglucose, magnesium aluminum silicate, maltodextrin, methylcellulose,polymethacrylates, povidone (e.g. Kollidon®, Plasdone®), pregelatinizedstarch, sodium alginate and starch.

The dissolution rate of a compacted solid pharmaceutical composition inthe subject's stomach may be increased by the addition of a disintegrantto the composition. Disintegrants include alginic acid,carboxymethylcellulose calcium, carboxymethylcellulose sodium (e.g.Ac-Di-Sol®, Primellose®), colloidal silicon dioxide, croscarmellosesodium, crospovidone (e.g. Kollidon®, Polyplasdone®), guar gum,magnesium aluminum silicate, methyl cellulose, microcrystallinecellulose, polacrilin potassium, powdered cellulose, pregelatinizedstarch, sodium alginate, sodium starch glycolate (e.g. Explotab®) andstarch.

Glidants can be added to improve the flowability of a non-compactedsolid agent and to improve the accuracy of dosing. Excipients that mayfunction as glidants include colloidal silicon dioxide, magnesiumtrisilicate, powdered cellulose, starch, talc and tribasic calciumphosphate.

When a dosage form such as a tablet is made by the compaction of apowdered composition, the composition is subjected to pressure from apunch and dye. Some excipients and active ingredients have a tendency toadhere to the surfaces of the punch and dye, which can cause the productto have pitting and other surface irregularities. A lubricant can beadded to the composition to reduce adhesion and ease the release of theproduct from the dye. Lubricants include magnesium stearate, calciumstearate, glyceryl monostearate, glyceryl palmitostearate, hydrogenatedcastor oil, hydrogenated vegetable oil, mineral oil, polyethyleneglycol, sodium benzoate, sodium lauryl sulfate, sodium stearyl fumarate,stearic acid, talc and zinc stearate.

In liquid pharmaceutical compositions of the present disclosure, themodulator of a eukaryotic pathogen's adenylyl cyclase and any othersolid excipients are dissolved or suspended in a liquid carrier such aswater, water-for-injection, vegetable oil, alcohol, polyethylene glycol,propylene glycol or glycerin.

Liquid pharmaceutical compositions may contain emulsifying agents todisperse uniformly throughout the composition an active ingredient orother excipient that is not soluble in the liquid carrier. Emulsifyingagents that may be useful in liquid compositions of the presentinvention include, for example, gelatin, egg yolk, casein, cholesterol,acacia, tragacanth, chondrus, pectin, methyl cellulose, carbomer,cetostearyl alcohol and cetyl alcohol.

Liquid pharmaceutical compositions of the present disclosure may alsocontain a viscosity enhancing agent to improve the mouth-feel of theproduct and/or coat the lining of the gastrointestinal tract. Suchagents include acacia, alginic acid bentonite, carbomer,carboxymethylcellulose calcium or sodium, cetostearyl alcohol, methylcellulose, ethylcellulose, gelatin guar gum, hydroxyethyl cellulose,hydroxypropyl cellulose, hydroxypropyl methyl cellulose, maltodextrin,polyvinyl alcohol, povidone, propylene carbonate, propylene glycolalginate, sodium alginate, sodium starch glycolate, starch tragacanthand xanthan gum.

Sweetening agents such as sorbitol, saccharin, sodium saccharin,sucrose, aspartame, fructose, mannitol and invert sugar may be added toimprove the taste. Flavoring agents and flavor enhancers may make thedosage form more palatable to the patient. Common flavoring agents andflavor enhancers for pharmaceutical products that may be included in thecomposition of the present disclosure include maltol, vanillin, ethylvanillin, menthol, citric acid, fumaric acid, ethyl maltol and tartaricacid.

Preservatives and chelating agents such as alcohol, sodium benzoate,butylated hydroxy toluene, butylated hydroxyanisole and ethylenediaminetetraacetic acid may be added at levels safe for ingestion to improvestorage stability.

According to the present disclosure, a liquid composition may alsocontain a buffer such as gluconic acid, lactic acid, citric acid oracetic acid, sodium gluconate, sodium lactate, sodium citrate or sodiumacetate. Selection of excipients and the amounts used may be readilydetermined by the formulation scientist based upon experience andconsideration of standard procedures and reference works in the field.

Solid and liquid compositions may also be dyed using anypharmaceutically acceptable colorant to improve their appearance and/orfacilitate patient identification of the product and unit dosage level.

The dosage form of the present disclosure may be a capsule containingthe composition, for example, a powdered or granulated solid compositionof the disclosure, within either a hard or soft shell. The shell may bemade from gelatin and optionally contain a plasticizer such as glycerinand sorbitol, and an opacifying agent or colorant.

A composition for tableting or capsule filling may be prepared by wetgranulation. In wet granulation, some or all of the active ingredientsand excipients in powder form are blended and then further mixed in thepresence of a liquid, typically water, that causes the powders to clumpinto granules. The granulate is screened and/or milled, dried and thenscreened and/or milled to the desired particle size. The granulate maythen be tableted, or other excipients may be added prior to tableting,such as a glidant and/or a lubricant.

A tableting composition may be prepared conventionally by dry blending.For example, the blended composition of the actives and excipients maybe compacted into a slug or a sheet and then comminuted into compactedgranules. The compacted granules may subsequently be compressed into atablet.

As an alternative to dry granulation, a blended composition may becompressed directly into a compacted dosage form using directcompression techniques. Direct compression produces a more uniformtablet without granules. Excipients that are particularly well suitedfor direct compression tableting include microcrystalline cellulose,spray dried lactose, dicalcium phosphate dihydrate and colloidal silica.The proper use of these and other excipients in direct compressiontableting is known to those in the art with experience and skill inparticular formulation challenges of direct compression tableting.

A capsule filling may include any of the aforementioned blends andgranulates that were described with reference to tableting; however,they are not subjected to a final tableting step.

EXAMPLES

The following examples further illustrate the disclosure, but should notbe construed to limit the scope of the disclosure in any way.

Example 1 I_(Ks) Function Requires ATP

I_(Ks) currents were examined by inside-out membrane patches fromXenopus oocytes at various intracellular ATP concentrations. Upon patchexcision, current ran down in low ATP (FIG. 2A), consistent withprevious findings that the loss of native ATP in cytosol resulted inreduced channel activity. See Loussouarn G. et al., EMBO J. 22, 5412(2003). However, the current ran up in the presence of higherconcentrations of ATP, suggesting that not all the channels expressed inthe membrane were active with the native cytosolic ATP that isinsufficient to saturate channel activation. Thus, a reserve of theI_(Ks) channels open in the presence of higher ATP concentrations,resulting in currents larger than that at the patch excision (FIG. 2A,B). The steady state current amplitude increased with ATP with the halfmaximal effective concentration (EC₅₀) at 1.7 mM (FIG. 2A, B), which isclose to the physiological ATP concentration in cardiac myocytes. SeeAllen, D. G. et al., J. Physiol 361:185 (1985); Eisner, D A., et al., JPhysiol 391:99 (1987); Stewart, L C., J Mol Cell Cardiol 26:1377 (1994).This result reveals that I_(Ks) is sensitive to the cellular energeticstate, and fluctuations of ATP such as in ischemia alters electricalproperties via regulating I_(Ks).

Example 2 The Physiological Importance of ATP Sensitivity of I_(Ks)

The physiological importance of I_(Ks) is supported by our subsequentfinding that Q357R in KCNQ1, a LQT-associated mutation identified inpatients who presented arrhythmic episodes during physical exercisereduces ATP sensitivity, as shown by an increased EC50 of ATP responseand the fraction of the currents activated by applied high ATP (FIG.2B). Here it is shown that channels composed of Q357R co-expressed withKCNE1 (Q357R I_(Ks)) produces a smaller current amplitude, a sloweractivation time course and a shift of the voltage dependence ofactivation toward more depolarized potentials as compared with the WTI_(Ks) channels measured from whole-cell currents. Each of these changesin channel properties decrease the contribution of I_(Ks) to thetermination of cardiac action potentials, resulting in prolongation ofaction potential duration. Furthermore, application of a highconcentration of ATP during inside-out patch clamp recordings of Q357RI_(Ks) restored the WT channel characteristics. Specifically, thecurrent amplitude increased 3- to 5-fold, accounting for all of thereduction in the whole cell current and the voltage dependence ofchannel activation shifted back toward less depolarized voltages tonearly superimpose with that of the WT I_(Ks) (FIG. 2C). These resultsshow that a decrease in ATP sensitivity of the I_(Ks) channel due tomutation Q357R leads to LQT-syndrome.

Example 3 KCNQ1 Expressed Alone without KCNE1 Shows a Similar DoseResponse to ATP (FIG. 2D)

This shows that the ATP dependence is an intrinsic property of KCNQ1 andnot altered by KCNE1 association. I_(Ks) channels also requirephosphatidylinositol 4,5-bisphosphate (PIP₂) for function and aremodulated by calmodulin (CaM) and phosphorylation of residues S27 andS92 in KCNQ1 by protein kinase A (PKA). However, the response of I_(Ks)currents to ATP did not change with reduced PIP₂, enhanced Ca²⁺ ormutations S27D/S92D that mimic phosphorylation (FIG. 2D), indicatingthat ATP activates the channel independent from these otherintracellular regulating molecules.

Example 4 KCNQ Channels Formed by Coexpression of KCNQ2 and KCNQ3 do notRequire ATP for Function

ATP activates the I_(Ks) channel by serving as the substrate forphosphorylation, binding to an associated protein or directly binding tothe channel proteins. To distinguish these mechanisms, the ability ofvarious nucleotides to prevent I_(Ks) current run-down was measured. GTPand a non-hydrolyzable ATP analog, 5′-adenylyl-β-β-imidodiphosphate(AMP-PNP), in the intracellular solution sustained channel function asdid ATP, while the rundown of I_(Ks) currents became progressivelyfaster when ADP and AMP were applied (FIG. 3A). Thus, ATP is not uniquein activating the channel and phosphorylation is not required.

On the other hand, an ATP analog biotin photoprobe, 2-azidoadenosine5′-triphosphate 2′,3′-biotin-long chain-hydrazone (AB11) (see Conner, SD et al., J Biol Chem (2005) 280: 21539) can be photo-cross-linked tothe KCNQ1 protein (FIG. 3B), indicating that the nucleotide directlybinds to KCNQ1 to modify I_(Ks) channel function. Here it is shown thatthe channels formed by co-expression of KCNQ2 and KCNQ3 do not requireATP for function (FIG. 3C), and AB11 cannot be photo-cross-linked to theKCNQ2 or KCNQ3 proteins (FIG. 3B).

Example 5 Location of the ATP Binding Cite in KCNQ1

To locate the ATP binding site in KCNQ1, chimera channels were analyzedby transplanting the cytosolic C-terminus to KCNQ2 and KCNQ3 to formQ2ctQ1 and Q3ctQ1. Similar to I_(Ks) channels formed by theco-expression of Q2ctQ1/Q3ctQ1 ran down after inside-out membrane patchexcision (FIG. 3C), suggesting that the chimeras acquire ATP sensitivityand the C-terminus of KCNQ1 contains the ATP binding site. Since thepotency of nucleotides in activating Ic correlates with the number ofphosphates (FIG. 3A) the channel associates with ATP throughelectrostatic interactions between basic residues and the negativelycharged phosphates of ATP. A mutational scan was performed to neutralizeeach of all the basic residues in the intracellular loops and theC-terminus of KCNQ1 to examine which of these residues affected ATPsensitivity.

The results revealed three mutations, R380S, K393M and R397W, thatreduced the expression of macroscopic I_(Ks) currents and ATPsensitivity (FIG. 3D, E). Residue R380 is located in Helix A that isdownstream from the S6 gate of the channel, whereas K393 and R397 arelocated in the linker between Helix A and Helix B (FIG. 3D). While eachof these mutations reduced ATP sensitivity, a combined mutationR380S/R397W eliminated ionic current altogether, although channelexpression in the plasma membrane could still be detected (FIG. 3E, F).Furthermore, R380S/R397W also eliminated photo-cross-linking of the ATPanalog AB11 (FIG. 3F). These results show that these three residues arepart of the ATP binding site, while each individual mutation reduces ATPbinding, the combined mutations disrupt ATP binding, resulting in theloss of channel function. Likewise, mutating each of these residues tonegatively charged amino acid residues, which could repel ATP, alsoeliminated ionic currents of I_(Ks) (FIG. 3E). A Mutational scan of eacharomatic residue in Helix A, B and the A-B linker identified onemutation, W379S, that eliminated ionic current and AB1photo-cross-linking of I_(Ks) (FIG. 3E, F), suggesting that W379 alsoparticipates in ATP binding. Interestingly, the mutations of theputative ATP binding site W379S, R380S, K393M and R397W are allassociated with LQTS, further revealing the physiological importance ofATP modulation of I_(K).

Example 6 ATP Binding Allows the Pore to Open and Co-Expression of KCNE1does not Alter this Fundamental Mechanism of ATP Dependent Activation

As a member of the Kv channel family, KCNQ1 is comprised of a voltagesensing domain (VSD) and a pore-gate domain (PD). The I_(Ks) channelcontains four KCNQ1 subunits with the VSD's surrounding a central poreacross the membrane; in response to membrane depolarization, voltagesensors move to trigger pore opening. See Larrson et al., PNAS (2010).Voltage clamp fluorometry (VCF) was used to investigate whether ATPbinding affects voltage sensor movements or pore opening; fluorescencesignals from a fluorophore (Alexa 488 C5 maleimide) attached to VSD (seemethods in Example 12, below) were recorded to monitor VSD movements,while ionic currents were simultaneously measured to show pore opening(FIG. 4A). The mutations that disrupt ATP binding, W379S and R380S/R397W(FIG. 3E), eliminated ionic currents of KCNQ1 but did not abolishΔF/Fsignals. Moreover, the F-V relationship is superimposed with that of theWT KCNQ1 (FIG. 4A), showing that ATP binding is not required for VSDmovements but necessary for subsequent pore opening. These results leadto a conceptual model for ATP dependent activation of KCNQ1 and I_(Ks)channels (FIG. 4D) such that ATP binding to the channel PGD is aprerequisite for the pore to open, but does not affect VSD activation.This experimental data of I_(Ks)-ATP dose response (FIG. 2B) and G-Vrelationship of I_(Ks) at various ATP's (FIG. 2C) shows that theco-expression of KCNE1 does not alter the fundamental mechanism of ATPdependent activation. The lack of influence of KCNE1 on ATP dependentactivation is also supported by the result that both KCNQ1 and I_(Ks)channels showed a similar response to ATP (FIG. 2D).

Example 7 The Q357R Mutation does not Alter the Fundamental Mechanism ofATP Dependent Activation

The disruption of ATP binding in the background of Q357R does not affectF-V relation (FIG. 4B). Q357 is located immediately C-terminal to the S6gate in KCNQ1 and away from the amino acids cluster that are importantfor ATP binding (FIG. 3D), yet it causes a reduction in ATP sensitivityof I_(Ks) activation (FIG. 2B). Although the WT I_(Ks) activationrequires ATP binding the properties of I_(Ks) activation includingsteady-state G-V relation (FIG. 2C) and time course of voltage dependentactivation and deactivation do not change with ATP, Q357R renders theG-V relation depending on ATP (FIG. 2C). While Q357R alters the slope ofF-V relation as compared to the WT KCNQ1 (FIG. 4A, B), the mutation doesnot change the properties of I_(Ks) G-V relation at high ATP (FIG. 2C),suggesting that a change in VSD movement may not relate to the change inATP dependence of G-V relations. This reveals that all these changes arenot brought by a direct influence of the mutation on ATP binding becauseunlike Q357R, mutations that directly affect ATP binding do not cause ashift of G-V relation to different voltages with the native ATP (FIG.4C). Interestingly, a simple change in the equilibrium constant of poreopening in the model (FIG. 4D) can recapitulate the mutation-causedchanges in ATP sensitivity (FIG. 2B) and ATP dependence of G-V relations(FIG. 2C). These results are consistent with the mechanism that ATPbinding regulates pore opening and a change in pore open probabilityallosterically alters the ATP regulation. Since all of the reportedmutations are associated with LQTS, these results show that mutations ofKCNQ1 can alter ATP dependent activation of the I_(Ks) channel withvarious mechanisms to cause human diseases.

Example 8 VSD Activation Occurs in the Absence of PIP₂

Using voltage-clamp fluorometry (VCF) on channels expressed in Xenopusoocytes, the effect of PIP₂ depletion on VSD activation and PD openingwas determined simultaneously. In VCF, fluorescent labeling of the S3-S4linker generates measurable changes in fluorescent intensity that arecorrelated with S4 movement during VSD activation; meanwhile,measurement of the whole cell ionic current detects PD opening. Herepseudo wild type (psWT)-C214A/G219C/C331A-Kv7.1 channels were used toavoid non-specific labeling of native C214 and C331 and labeled positionG219C with Alexa 488 C5 maleimide. See Osteen, J D et al., PNAS107:22710 (2010). To deplete PIP₂, CiVSP, a voltage-sensing lipidphosphatase that rapidly dephosphorylates PIP₂ upon membranedepolarization was expressed in cells according to the protocol providedin Murata, Y. et al., Nature 435:1239 (2005). When CiVSP was activatedwith a train of six depolarizing (+60 mV) pulses, the psWT channelcurrent was robustly inhibited. In clear contrast, the magnitude of thefluorescence signal change (ΔF/F) was unaltered by CiVSP, indicatingthat VSD activation still occurs after PIP₂ depletion. As an alternativemethod to VCF, VSD activation was analyzed using MTSES(2-sulfo-natoethyl methanethiosulfonate) modification of I230C in S4,which is only accessible to MTSES when the VSD is activated. See, forexample, Murata Y, et al. (2005). This experiment confirmed that VSDactivation occurs in the absence of PIP₂. After PIP₂ depletion, thesteady-state voltage-dependence of VSD activation, reflected in thefluorescence-voltage (F-V) relationship, was unchanged, while the ioniccurrents were inhibited. Altogether, these results demonstrate that PIP₂is not required for detection of membrane voltage within the VSD.

Example 9 PIP₂ is Required for Coupling

Applicants' tested whether PIP₂ is required for coupling. Coupling wasquantified by measuring the effect of VSD activation on PD opening or bymeasuring how PD opening affects VSD activation. See Ryu, S., 140:469(2012). This approach enables the measurement of VSD activation afterPIP₂ depletion when PD opening became undetectable. In order to promotepore opening, the mutation L353K was introduced into the S6 gate.psWT/L353K channels conducted instantaneous current at every voltage weapplied, and these currents were not reduced when we expressed andactivated CiVSP. Furthermore, psWT/L353K currents reversed near K⁺equilibrium and were reduced when the Kv7.1 pore blocker chromanol 293Bwas applied according to the methods disclosed in Lerche, C. et al.,71:1503 (2007), which provides evidence that the observed constitutivecurrents were indeed conducted by expressed psWT/L353K channels. Bycomparing the VSD activation of psWT and locked open psWT/L353K channelsVSD-PD coupling was detected directly as a leftward shift in the F-Vrelationship. This shift is consistent with the positive couplingbetween VSD activation and PD opening, i.e., less energy is required toactivate the VSD if the PD is open. When PIP₂ was depleted using CiVSP,the psWT/L353K channels remained open, but their F-V relationship nolonger differed from psWT channels. This showed that PIP₂ is requiredfor PD opening (by L353K) to promote VSD activation.

Next other mutations were tested to determine whether PIP₂ is requiredto affect VSD activation and two such mutations (e.g., S349A, G350A)were identified. S349A, G350A, and L353 are located in the S6 gate, andhomology modeling predicted that they do not interact with the VSD orthe S4-S5 linker. This reveals that these mutations directly alter PDopening and indirectly affect VSD activation through PIP₂-dependentcoupling. Thus, the data provided herein clearly show that PIP₂ isrequired both for VSD activation to cause PD opening and for PD openingto affect the activation of the VSD. Taken together, these findings showthat a membrane lipid is required for the functional coupling betweenthe VSD and the PD.

Example 10 Identification of the PIP₂ Binding Site

A critical step to understanding how PIP₂ binding mediates VSD-PDcoupling was to identify its binding site. Using a Kv7.1 homology model,16 basic residues that are located near VSD-PD interface wereidentified. These residues are highly conserved among the Kv7 channels,which require PIP₂ for voltage-dependent gating, but are poorlyconserved among other Kv channels that do not require PIP₂ (FIG. 8A).Using site directed mutagenesis, each of these basic residues in WTKv7.1 were individually neutralized and the effect on the expressedcurrent amplitude was measured using two-electrode voltage clamp.Because the endogenous level of PIP₂ in the oocyte membrane is withinthe sensitive range of Kv7.1 a reduction of PIP₂ sensitivity by anymutation is will reduce Kv7.1 currents. The data reveal that eightmutations (R190Q, R195Q, H258N, R259Q, K354N, R360Q, H363N, R366Q)severely decreased (>50% reduction, FIG. 8B, C blue) the whole cellcurrent amplitude and four mutations (R192Q, R243Q, K358N, K362N) thathad a milder reduction (<50% reduction, FIG. 8B,C green). Conversely,four neutralizing mutations (R181Q, K183N, K196N, R249Q) and threeadditional charge-reversing mutations (R249E, K358E, R360E) actuallyincreased the current amplitude (FIG. 8B, C, red). Notably, robustsurface expression of the loss-of-current mutants by Western Blotanalysis of proteins labeled by extracellular biotin (FIG. 8D) wasdetected showing that loss of current expression is not due to reducedprotein synthesis or membrane trafficking. Furthermore, fluorescentsignal changes in VCF measurements for all of the loss-of-currentmutations (FIG. 8E, 9) were observed indicating that these mutantchannels not only expressed to the membrane, but also retained VSDactivation. Therefore, the loss-of-current mutations affected channelgating by decreasing coupling is consistent with decreased PIP₂ binding,or by decreasing PD opening.

Next, the mutations identified were examined for their ability to affectcurrent amplitude by changing the apparent PIP₂ affinity. Applicants'measured the time course of the current rundown that occursspontaneously as phosphoinositides are lost from excised membranepatches. Applicants' found that the effects of mutations (K358N, K362N,R181Q, K183N, R249Q, R249E) on the time course of rundown after patchexcision were correlated with their effects on expressed currentamplitude. That is, relative to WT channels, the rundown was faster forthe mild loss-of-current mutations and slower for the gain-of-currentmutations (FIG. 8F-G). These results further support the finding thatthe mutations of conserved basic residues at the VSD-PD interface affecta PIP₂ mediated process that is required for channel function.

Next, the strength of VSD-PD coupling for several of the mutationsidentified herein was directly quantified including, but not limited to,R192Q, R195Q, K196E, K358N, K358E, R360Q, R360E, K362N, H363N, R366Q bymeasuring the F-V shift caused by locking the PD open with L353K. Themutations influenced VSD-PD coupling in a manner that was correlatedwith their effect on the expressed current amplitude i.e., theloss-of-current mutations decreased the magnitude of the F-V shift,while the gain-of-current mutations increased the F-V shift (FIG. 9A-D).Strikingly, the equilibrium model predicted this relationship when thebinding constant for PIP₂ (K_(PIP2)) (FIG. 9 D, black line) was varied.Taken together, these results suggest that these mutations disruptVSD-PD coupling and decrease channel current by directly affecting PIP₂binding.

Applicants mapped these data onto a Kv7.1 homology model and found acluster of severe loss-of-current residues at the VSD-PD interface thatincludes R190 and R195 in the S2-S3 linker, H258 and R259 in the S4-S5linker, and K354 in the proximal C terminus. In the experiments herein,these mutations mimicked the effects of PIP₂ depletion on psWT channels:they severely inhibited the ionic current, did not prevent VSDactivation, and greatly diminished the VSD-PD coupling. Therefore, thiscluster of basic residues constitutes a critical interaction site forPIP₂ mediated coupling. These findings show that applicants haveidentified site is a PIP₂ binding site that is conserved amongvoltage-dependent and voltage-independent K⁺ channels.

PIP₂ mediated coupling in Kv7.1 has direct implications for humanpathophysiology. In the heart, Kv7.1 subunits co-assemble with KCNE1accessory subunits to generate the slow delayed rectifier current(I_(Ks)) that regulates the duration of the cardiac action potential.Inherited loss-of-function mutations of Kv7.1 and KCNE1 are associatedwith Long-QT Syndrome (LQTS), in which the ventricular action potentialduration is prolonged, resulting in a high risk of ventriculararrhythmias and sudden death. Many LQTS associated mutations affect thebasic residues in the PIP₂ pocket for example, R190Q, R190W, 258N,H258R, R259H, R259C, R259L, R360T, R366Q, R366W, R366P. For thesemutations, loss of VSD-PD coupling compromises the I_(Ks) channelfunction and create a substrate for cardiac arrhythmias. The resultsdemonstrate that modifiers of VSD activation will not rescue channelfunction for these mutations. Furthermore, drugs that force the PD openwill abolish the voltage- and time-dependence of the I_(Ks) current thatis critical for the timing of the action potential. Thus, a drug thattargets PIP₂ dependent coupling amplifies current without losing thesephysiologically important characteristics.

Example 11 Voltage Dependent Activation is Sensitive to ChargePerturbations at the E1 Position

Like most voltage-dependent channels, Kv7.1 contains two conservedglutamates in S2 (E1 and E2) and a series of arginines in S4 (R1, R2,etc.) (FIG. 1A). However, Kv7.1 has a glutamine (Q3) at what is thethird arginine position and a histidine (H5) at what is the fiftharginine position in other Kv channels. Applicants found that E1K orE1K+KCNE1 generates current indistinguishable from background currentexpressed by native oocyte channels without or with KCNE1 (<0.5 or <2μA, respectively), and much smaller than wild-type (WT) Kv7.1 or WTKv7.1+KCNE1 currents, revealing that E1K channels themselves do notgenerate any current. A similar charge reversal mutation, E1R, exhibitsan identical phenotype to E1K. When E1 was conservatively mutated to thenegatively charged aspartate or mutated to the electrically neutralglutamine, cysteine, or alanine, all formed functional channels,although E1A reduced current (FIG. 1B). Neutralizing mutations allshifted the G-V relationship rightwards (FIG. 1C), revealing thatremoval of the negative charge at E1 hinders channel activation. Only apositive charge at E1 completely abolished current. These results showthat the loss of current is caused by the inability of E1K/R channels toopen, through disruption of electrostatic interactions involving E1 andnot due to a trafficking defect.

Inspection of the sequence of Kv7.1 and KCNE1 reveals that the argininesin the S4 segment of Kv7.1 are the only positively charged residues inthe membrane-spanning segments. E1R paired with R1E, R2E, Q3E, or R4Egenerated currents significantly larger than currents from E1R alone(FIG. 1D, E). While, S0E, H5E, and R6E that flank these four residuescould not rescue any current (FIG. 1E). These data show that E1interacts electrostatically not only with R4, but also with R1 and R2.Q3 is also positioned to interact with E1 through hydrogen bonding innative channels. Restoring electrostatic attractions between specificresidues and E1R allows S4 to occupy an activated conformation so thatchannels can open, albeit with properties different from WT channels.All the rescued currents except for E1R/Q3E changed instantaneously inresponse to voltages from −120 to +60 mV (FIG. 1D). These currents havereversal potentials that approach the K⁺ equilibrium potential (80-90mV) and are be blocked by the Kv7.1 pore-blocker chromanol 293B,confirming that these are K⁺ currents carried through the conductionpore of constitutively open channels.

Example 12 Materials and Methods

Mutagenesis.

Site-directed mutations were introduced using overlap extension and highfidelity PCF. DNA sequencing confirmed each mutation. RNA was made by invitro transcription using the mMessage mMachine T7 polymerase kit(Applied Biosystems).

Channel Expression.

9.2 ng of channel cRNA was injected, using Nanoject (Drummond), intoeach of stage V-VI, defollicuated oocytes from Xenopus laevis. Forexpression of CiVSP, 2.3 ng of CiVSP RNA was injected simultaneously.The cells were incubated at 18° C. for 4-7 days for robust expression inND96 solution [in mM: 96 NaCl, 2 KCl, 1.8 CaCl₂, 1 MgCl₂, 5 HEPES, 0.3K2EDTA].

Electrophysiology.

Two-electrode voltage clamp: Whole-cell currents were recorded fromoocytes bathed in ND96 solution using a CA-B amplifier (Dagan) intwo-electrode voltage clamp mode. Microelectrodes were pulled to aresistance of 0.3-3 MΩ and filled with 3 mM KCl. Signals were sampled at1 KHz using the Patchmaster acquisition software (HEKA). The holdingpotential was set to −80 mV throughout unless otherwise specified.

Voltage-clamp fluorometry: For VCF, oocytes were labeled on ice for 45minutes in 10 μM Alexa 488 C5 Maleimide (Life Technologies) in highpotassium depolarizing solution [in mM: 98 KCl, 1.8 CaCl2, 1 MgCl2, 5HEPES, PH 7.6]. The cells were washed with ND96 and kept on ice untilVCF recording. Fluorescent signals were recorded simultaneously with thewhole cell (TEVC) currents in ND96 solution, using a DLMFS (Leica)upright microscope through a FITC filter cube (Lieca). Light from astandard 100W halogen bulb was focused onto the animal pole of theoocyte and emission from the cube was focused on a P20A photodiode. Thecurrent from the photodiode was amplified using an EPC10 patch amplified(HEKA), low pass filtered at 200 Hz and sampled at 1 KHz usingPatchmaster (HEKA).

Patch clamp: Inside-out membrane patches were formed using patchelectrodes pulled to 0.5-1 MΩ and filled with pipette solution [in mM:140 KMeSO3, 20 HEPES, 2 KCl, 2 MgCl2, PH 7.2] and excised into thebathing solution [in mM: 140 KMeSO3, 20 HEPES, 2 KCl, 5 EGTA, 1.5 mMMgATP, PH 7.2]. Macroscopic currents were recorded, at room temperature,using an Axopatch 200-B amplifier (Axon Instruments) driven by the Pulse(HEKA) acquisition software. Current were digitized at 1 KHz. Allrecordings were made in room temperature (20-22° C.).

Data Analysis.

The baseline fluorescence was fit with a line during the 2 seconds atthe −80 mV holding potential that preceded each test pulse. This linearbaseline approximation was extrapolated to the duration of the pulse andΔF/F was calculated as (F(t)−F_(baseline)(t))/F_(baseline)(t) where F(t)is the fluorescent intensity at time t (AU) and F_(baseline)(t) is theextrapolated baseline value at time t. The Boltzmann equation was usedto fit the fluorescence-voltage relationships: NormalizedΔF(V)=PVa(V)=1/(1+exp(−z*F*(V−V_(1/2))/RT) where PVa is thevoltage-dependent probability of the voltage sensor assuming theactivated state, V is the test voltage (V), V_(1/2) is the voltage ofhalf maximal voltage sensor activation, z is the number of elementarycharges translocated across the membrane upon VSD activation, R is thegas constant (J/K/mol), and F is the faraday constant (C/mol).

Chemical Modification.

2-sulfo-natoethyl methanethiosulfonate (MTSES, Toronto ResearchChemicals) was dissolved in DMSO at 100 mM, aliquoted and frozenimmediately. Aliquots were thawed just prior to use and added directlyto bath solution in a bolus to achieve the desired final concentration.

Biotinylation:

Membrane expression was detected through biotinylation and Western blot(see Wu et al., Journal of General Physiology. (2010)). Cell surfaceproteins of intact oocytes were labeled with 1 mg/ml ofSulfo-NHS-SS-Biotin (Thermo Scientific). The cells were washed,homogenized, and incubated with Neutravidin beads (Thermo Scientific) topull down biotin labeled proteins. The pulled down proteins were probedvia Western blot using a Kv7.1 antibody (Santa-Cruz Biotechnology) or aGP antibody to test for labeling of cytosolic proteins.

What is claimed is:
 1. A method of treating Long-QT syndrome (“LQTS”) ina subject in need thereof comprising administering an effective amountof an agent that modulates the activity of a KCNQ channel, wherein saidagent is C28.
 2. The method of claim 1, wherein said KCNQ channel is anI_(Ks) channel.
 3. The method of claim 2, wherein the agent modulatesI_(Ks) channel activity by altering voltage dependent activation of theI_(Ks) channel.
 4. The method of claim 1, wherein said KCNQ channel isan M-channel.
 5. The method of claim 4, wherein the agent modulatesM-channel activity by altering voltage dependent activation of theM-channel.
 6. The method of claim 1, wherein said KCNQ channel is KCNQ4channel.
 7. The method of claim 6, wherein the agent modulates KCNQ4channel activity by altering voltage dependent activation of KCNQ4channels.
 8. The method of claim 1, wherein the agent modulates KCNQchannel activity by altering ATP binding to the KCNQ channel.
 9. Themethod of claim 8, wherein the agent modulates KCNQ channel activity byaltering ATP binding to the KCNQ channel by interacting directly with asegment of the KCNQ1 protein comprising the amino acid sequence setforth in SEQ ID NO:
 25. 10. The method of claim 1, wherein the agentmodulates KCNQ channel activity by altering PIP₂ binding to the KCNQchannel.
 11. The method of claim 1, wherein the agent increases KCNQchannel activity.
 12. The method of claim 1, wherein the agent reducesKCNQ channel activity.